Bohr's contributions to physics

The theory that electrons travel in discrete orbits around the atom's nucleus, with the chemical properties of the element being largely determined by the number of electrons in each of the outer orbits.

The idea that an electron could drop from a higher-energy orbit to a lower one, emitting a photon (light quantum) of discrete energy (this became the basis for quantum theory).

Bohr also conceived the principle of complementarity: that items could be separately analyzed as having several contradictory properties. For example, physicists currently conclude that light is both a wave and a stream of particles - two apparently mutually exclusive properties - on the basis of this principle. Bohr also found philosophical applications for this daringly original principle. Albert Einstein much preferred the determinism of classical physics over the probabilistic new physics of Bohr (to which Max Planck and Einstein himself had contributed). He and Bohr had good-natured arguments over the truth of this principle throughout their lives (see Bohr Einstein debate). One of Bohr's most famous students was Werner Heisenberg, a crucial figure in the development of quantum mechanics, who was also head of the German atomic bomb project.

Niels Bohr and his wife Margrethe had six children. Two died young, and most of the others went on to lead successful lives. One, Aage Niels Bohr, also became a very successful physicist; like his father, he won a Nobel Prize.

Later years / Death / Legacy

In 1941, during the German occupation of Denmark in World War II, Bohr was visited by Heisenberg in Copenhagen (see next section). In 1943, shortly before he was to be arrested by the German police, Bohr escaped to Sweden, and then traveled to London.

He worked at the secret Los Alamos laboratory in New Mexico, USA, on the Manhattan Project, where, according to Richard Feynman, he was known by the assumed name of Nicholas Baker for security reasons. His role in the project was important. He was seen as a knowledgeable consultant or "father confessor" on the project. He was concerned about a nuclear arms race, and is quoted as saying "That is why I went to America. They didn't need my help in making the atom bomb." [1].

The element bohrium is named in his honor. He is pictured on the 500 kr. Danish bank note.
In 1965, three years afters Bohr's death, the institute of physics at the university of Copenhagen changed name to the Niels Bohr Institute.

Kierkegaard's influence on Bohr

It is generally accepted that Bohr read the 19th century Danish philosopher Søren Kierkegaard. In 1909, Bohr sent his brother Kierkegaard's Stages on Life's Way as a birthday gift. In the enclosed letter, Bohr wrote, "It is the only thing I have to send; but I do not believe that it would be very easy to find anything better.... I even think it is one of the most delightful things I have ever read." Bohr enjoyed Kierkegaard's language and literary style, but mentioned that he had some "disagreement with [Kierkegaard's ideas]". [2]

Given this, there has been some dispute over whether or not Bohr's philosophy and science were influenced by Kierkegaard. David Favrholdt argues that Kierkegaard had minimal influence over Bohr's work; taking Bohr's statement about disagreeing with Kierkegaard at face value, while Jan Faye argues the opposing point of view; by arguing that one can disagree with the content of a theory while accepting its general premise and structure. Template:NamedRef

Relationship with Heisenberg

Werner Heisenberg claimed in an interview after the war, when the author Robert Jungk was working on the book Brighter Than a Thousand Suns, that he had tried to establish a pact with Bohr such that scientists on neither side should help develop the atomic bomb. He also said that the German attempts were entirely focused on energy production, and that his circle of colleagues tried to keep it that way. Heisenberg nuanced his claims, though, and avoided implication that he and his colleagues had purposely sabotaged the bomb effort. However, this nuance was lost in Jungk's original publication of the book, which strongly implied that the German atomic bomb project was rendered purposely stillborn by Heisenberg.

When Bohr saw this depiction in the Danish translation of Jungk's book, he disagreed wholeheartedly. He said that Heisenberg had indeed let him know in Copenhagen that he was working on an atomic bomb project, and that he thought that Germany would win the war. He dismissed the idea of any pact as an after-the-fact construction. He drafted several letters to inform Heisenberg about this but never sent any of them.[3]

Michael Frayn's play Copenhagen, which ran on Broadway for a time, explores what might have happened at the 1941 meeting between Heisenberg and Bohr. The truth of the historical event is still a matter of scholarly debate, as neither Bohr nor Heisenberg spoke about it in any detail, and they were alone in the woods.